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Older honda 100 running barley

mschaeff8

New member
"I just purchased a Honda 100

"I just purchased a Honda 100 with a blue and white lid (1980's?). It starts up great. It will run at full throttle for awhile, then it will down power to a level of power that is bellow what you get from minimum throttle - though the prop continues to turn and push the boat very slowly. When it does this the engine shakes rather aggressively and it runs louder and occasionally pops like it is missing. The motor will at intermittent times return to full power for varying lengths of times (though never more then ten min. at a time). This motor may have been sitting outside for a year unused (I did use new gas). Any ideas? The help is very much appreciated."
 
Check to see if it runs better

Check to see if it runs better with the cover off.

These engines are noted for getting a hole in the (hard to see) exhaust pipe between the head and the lower case.

Runs great until it starts gasping on its own exhaust.
 
Discovered by accident a good

Discovered by accident a good test for the exhaust extension was to fill up the bottom of the engine cowling with water and look for bubbles. (not past the powerhead gasket).

Along the same line is the evaporative controls built into the motor ending in the big lump ahead of and below the starter. The small hose and the form fitted hose get little cuts in them due to hondas love of spring wire hose clamps.
 
"Agree with Pilotart and Willi

"Agree with Pilotart and William. But if those issues don't emerge, then I would go back to the fuel system. Check all hoses & connections, remove and clean all fuel filters, especially the high pressure filter (if that engine has one), make sure that the fuel tank is breathing properly - run it with the fuel tank lid lossened to make sure you are not creating a vacuum on the back side of the fuel line."
 
Thanks for the input guys! I&

Thanks for the input guys! I'm going to check out all these things this week and will post what I find.

W D: how do I determine if the tank is breathing properly?
 
"Depends on the type tank you

"Depends on the type tank you have - I assume you are using a built in tank. There will be a breather tube that typically exits just below the starboard gunwale, near your fuel filler cap. You need to make sure air freely runs through that tube. Some folks will run a wire thru it. I prefer blow compressed air through the fuel filler (sealed with a shop rag) and make sure I get a good flow of air out the breather tube."
 
"We had a 15hp that ran funny

"We had a 15hp that ran funny and pooped and slowly died and it turned out to have a worn cam lobe. Just a thought. (also effected the ignition!)

You should have a remote tank with a frosted over fuel level gauge in the cap with a knurled nut right in the middle. That is your tank vent. To see if your line is collapsed, you will have to blow from the tank towards the motor as the primer bulb had check valves. Don't use compressed air as the fuel pump can not handle the pressure. -works good on integrated tanks, but not on remote.

If you need a cam I have a parts motor."
 
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